Gates' office said he still plans to promote the book in a series of appearances.

Veterans of the Barack Obama and George W. Bush presidencies are waiting to see what Gates has to say. Gates led the Pentagon during both administrations, amid controversies over Iraq, Afghanistan, and the war on terrorism.

"Dr. Gates accidentally fell at his home in Washington State Wednesday evening and fractured his first vertebrae. He was treated at hospitals in Mount Vernon (Wash.) and Seattle and is now back at home with his family resting comfortably.

"He is expected to make a full recovery and thanks the medical staffs of both hospitals for the excellent care they provided him. He looks forward to the release of his new memoir 'Duty' on January 14th, which he will be promoting wearing a neck brace."